Debayering

[jambouk]

Typing "what is debayering" into Google isn't yielding much useful information.

1. Am i right in thinking this is the step/process where the three images (red, green and blue) taken by a one shot colour camera are merged into one colour image?

2. On my new colour cmos camera (ASI120MC), and using firecapture software, there is a box to check which says "debayer". If i uncheck this, the resultant image is monochrome. Which of the three set of pixels is this monochrome image taken from (red, green or blue)?

Thanks

James

[Cornelius Varley]

1. you are correct in your thinking.

2. The mono image is a grayscale representation of the colour values of all the r g b bayer matrix. When you select the option to debayer the image is captured as mono but the colour information is retained for processing into a full colour image later. This way the capture frame rate can be higher than a colour video capture because the camera doesn't need to convert the video stream to colour in realtime.

[jambouk]

That's interesting. So:

3. Is the resolution of an image (or video) shot in ''mono mode' on my (or other OSC) camera(s) greater than those shot in colour mode?

4. Does the camera/computer just ignore the inbuilt coloured filters above the pixels? So if red light hits a red pixel it is just interpreted as white light, and so on, and if red light hits a blue pixel it can't get through so its not interpreted as anything?

5. If i took a 2 minute *.avi video of Saturn in 'mono mode', at a higher frame rate than colour mode would allow, how would i then add back in the colour before processing in registax or other stacking software?

James

[jambouk]

I've just played with my camera.

Interestingly, turning off debayering (making it mono) doesn't increase the frame rate capability with my chosen 640x480. Both are about 60-70 fps. The mono image on screen at least is much more grainy.

This isn't as straight forward as I thought.

James

[jambouk]

Here are two screen shots from liveview zoomed in to 300% with the visual (fisheye) lens on the camera in the dining room; the only setting I changed were the bayered box being ticked or not:

[Arecibo]

If your camera can give selectable colour and monochrome information, it's possible that it "tricks" the monochrome image.

I'm not sure of technological possibilities, but can´t think of a reliable way to remove the colour Bayer matrix (which is a physical array of filters, one for each primary -RGB- and pixel), and put it back again, under software control.

What possibly occurs is that, when monochrome selected, it "integrates" four pixels (perhaps three, for a rather uncommon Bayer matrix), each filtered differently into a "superpixel" with just the luminance of the tricolour array. Or replicates this luminance on the four original pixels.

Do you have the same resolution, independent of setting?

A third possibility is that the monochrome option gives the, so to say, RAW signal in the pixels (irrespective of which filtered pixel the signal comes from). In this case, the colour information is recoverable, but you'll see heavy graininess due to different sensibilities to band filtered light.

If the monochrome looks some how "checkered", I'd bet for the third option. You can improve the checkerboard look by shooting (in monochrome) to a red (or green, or blue) target (coloured paper, for example).

I had to follow that route to be able to use (to process) the RAW images produced by my Canon DSLR.

[jambouk]

Checker board, yes! It sounds like option three.

There is then, no advantage to me shooting in monochrome, as the frame rate is not improved, and the resultant image appears to contain less resolution.

Thank you.

James

[Arecibo]

You're welcome

And I do concur, if the camera is giving you de RAW sensor signal, there's no advantage in shooting in monochrome. Possibly it's just a marketing mirage (to make it appear more versatile than it really is).

(Peter is right in one respect: by using monochrome, you relieve the camera from computing the RGB from the RAW; I'm not sure if that matters or not; it depends on the kind of processor it has. It may happen that the conversion is not done in the camera, but by the capture software. And, then, it does not matter at all -unless you're using an old computer, with low processing power-).

Be warned (and I'm still assuming that our interpretation of what happens is right) that working in colour mode you don't get more resolution (than in monochrome). But it's a rather convolved subject, with a long detour into Math, Colour Perception, etc.

I regularly use the RAW sensor signal of Canon DSLRs (a 60Da, now on repair, and a 1100D), with a Bayer 2x2 matrix, with one RED pixel, two GREEN pixels, and one BLUE pixel. And get better results by making an RGB superpixel (reducing the resolution by a 2 factor).

[lensman57]

Typing "what is debayering" into Google isn't yielding much useful information.

1. Am i right in thinking this is the step/process where the three images (red, green and blue) taken by a one shot colour camera are merged into one colour image?

2. On my new colour cmos camera (ASI120MC), and using firecapture software, there is a box to check which says "debayer". If i uncheck this, the resultant image is monochrome. Which of the three set of pixels is this monochrome image taken from (red, green or blue)?

Thanks

James

Hi James,

I have an ASI 120 MC too which I now use for guiding. I believe that all ccd chips are essentially monochrome. For a colour image to form, the wafer is topped with an array of 2x green and one of each of red and blue filters, Bayer matrix, if you like to call them. The reason for 2x green is to try and mimick the human's eye's resopnse to green light compared to red and blue. Each filter will then blocks all other wavelenght and only pass on the corresponding one to the chip. This information from the chip is then deciphrered by the onboard processors in the case of a DSLR or software in case of webcams to reconsititue the colour image and this is called debayreing as the colour matrix on top of the chip is a Bayer matrix. The monchrome option may be of use for a sort of "synthetic LRGB" processing using the RGB capture or for guiding unding fire catpture .

A.G

[jambouk]

Thank you.

James

[mherman346]

If you capture using FireCapture 2.3, you should leave the DeBayer option turned off.

This saves the video in the smallest file size.

Later, you want to use the FireCapture program "Debayer.exe" and choose the "GB" method for video created by the ZWO ASI120MC video camera.

There are 7 options to DeBayer.  I was told by an experienced planetary imager that the "AdaptiveSmoothHue" should work best. 

If you capture with DeBayer turned on, the files will be full RGB color, and will be about 3X the size of storing the un-DeBayered raw video.

You must DeBayer the video file before doing image stacking.  So in the end you will end up with both the raw Bayer video and the 3X sized DeBayered color video too.

Best regards,

Michael

[jambouk]

Michael

So is the only difference you are describing a file size difference? Is there any difference in the end result/quality of the data?

Regards

James

[lensman57]

Typing "what is debayering" into Google isn't yielding much useful information.

1. Am i right in thinking this is the step/process where the three images (red, green and blue) taken by a one shot colour camera are merged into one colour image?

2. On my new colour cmos camera (ASI120MC), and using firecapture software, there is a box to check which says "debayer". If i uncheck this, the resultant image is monochrome. Which of the three set of pixels is this monochrome image taken from (red, green or blue)?

Thanks

James

Hi,

All CCDs are monochromatic, the reason you get colour is because of the Bayer Matrix array filter that is on the top of a "colour" CCD. These arrays  are 1XR, 1XB and 2XG, the reason for 2G is to mimick the response of the human eye to the spectrum. In a mono camera all ccd sites capture the photons from the target,in a colour CCD the Matix will filter the corresponding light falling on the sensor, it is therefore easy to deduct that the resolution and sensitivity of two identical sensors  will be much greater for the mono CCD. This is the main reason that most folks doing DSO imaging have atleast a mono camera. The data from a mono CCD can produce colour image if one uses an RGB imaging routine through the corresponding filters, these subs will then be combined post capture to form a colour, RGB image. The data from a Colour CCD will have to be debayered either by on camera hardware or by software to produce a colour image, a raw data file from a colour CCD will be in mono but the bayer marix pattern still visible as a grid on top the image with high magnification. I am not familliar with fire capture and see no advantage in having an unbayered captunless this data is "Binned" to increase sensitivity for focusing routine at a great expense to resolution. This method is used for example in my Atik 428EX OSC during a frame and focus routine. Hope that this helps.

Regards,

A.G

[glappkaeft]

So is the only difference you are describing a file size difference? Is there any difference in the end result/quality of the data?

There can be a difference in result but only in a round about way. The smaller amount of data the camera need to send per image using RAW (typically 1 byte/pixel for RAW and 3 bytes/pixel for uncompressed RGB) often allows the camera to record at a higher frame rate. If there is no other bottleneck this allows you to record either sequences with more frames or more sequences which is a good thing. This is the only real reason to prefer RAW over uncompressed RGB. 

[jambouk]

I cam get probably get towards 60 fps for Jupiter at colour, so i don't think there is an advantage for me to debayer then.

(This was an old thread i'd forgotten about, and which i'd started when i got my planetary camera earlier in the year)